Alkali method for leaching vanadium from a vanadium-containing chromium mud

Vanadium is an important strategic resource. In our country, and vanadium compounds are two main sources, i.e., magnet vanadium and titanium ore and stone coal. Although some vanadium-containing wastes produced in some industrial processes related to vanadium do not have an advantage in terms of quantity, from the perspective of resource recycling, research on the vanadium extraction of such waste vanadium resources is also of great significance.

According to the different characteristics of vanadium resources, the vanadium extraction process is also different. For stone coal and vanadium-containing clay , the traditional vanadium extraction mainly uses sodium roasting-water immersion, calcification roasting-acid leaching and blank roasting-acid leaching processes, and many mechanisms have been adopted for the mechanism, especially the mechanism of the roasting process. Research reports were carried out. In addition, some scholars have studied from the perspective of roasting method, proposed a new process of microwave roasting-water leaching vanadium, and discussed the mechanism of microwave roasting. Due to some shortcomings in the roasting process, such as the generation of polluting gases, low conversion rate and high energy consumption, the focus of the vanadium extraction process has shifted to wet acid leaching, and some progress has been made in its process and mechanism. At the same time, some studies have shown that direct acid leaching of some vanadium-containing resources requires a larger amount of acid to obtain a higher vanadium leaching rate, which is extremely difficult to operate in the subsequent steps of extracting vanadium. Another scholar studied the vanadium extraction process under pressure and found that vanadium can be dissolved with low acid, but the industrialization of this process is difficult due to equipment limitations. Due to the good selectivity of the alkali leaching process and the low requirements on equipment, it has attracted the attention of many scholars. Navarro, He Dongsheng et al. conducted an alkali leaching study on the characteristics of their respective vanadium resources.

For vanadium-containing waste resources, because of the large differences in their production pathways, even vanadium resources of the same type may have many differences in physical properties, chemical composition and structure. Therefore, research on vanadium extraction of such vanadium-containing resources is required. More targeted, in order to achieve the goal of process optimization. In this paper, an exploratory experiment was carried out on the characteristics of a vanadium-containing chrome mud, and then a single-factor experiment of alkali leaching was carried out. Based on this, a preliminary experiment of oxidative leaching was carried out.

First, experimental materials and methods

(1) Experimental materials

The vanadium-containing chrome mud is taken from a company in Panzhihua. The original slag contains more water. After drying at 105 °C, elemental analysis is carried out. The results are shown in Table 1.

Table 1 Chemical composition of vanadium-containing chromium mud (mass fraction) /%

(two) experimental principle

During the leaching process, the pH value has a great influence on the existence and behavior of V(V) in the solution. The specific performance is as follows:

For V(V), the acid leaching must be such that the pH is <1.5, and the alkali leaching must ensure that the OH ^- ion concentration is sufficiently large to displace the VO ₃ ^- combined with the cation to cause dissolution.

For V (W), at pH = 6.7 ~ 11.5 does not dissolve, <VO ₂ ⁺ ion form can be eluted in the acidic solution 6.7, at pH> 11.5 at a pH in the alkaline stripping solution occurs following reaction:

VO ₂ ⁺ +3OH ^- → VO(OH) ₃ ^-

(3) Experimental methods

An exploratory experiment of vanadium leaching of vanadium-containing chromium mud was first carried out. When leaching, weigh 100g of vanadium-containing chromium mud into a three-necked flask placed in a water bath, and add a certain liquid-solid ratio (the ratio of the leaching agent volume (mL) to the vanadium slag mass (g)) to a predetermined concentration. The leaching agent, the amount of leaching agent is the mass fraction of the leaching agent and the ore sample. Control leaching temperature and leaching

between. After the completion of the leaching, the V ₂ O ₅ concentration in the leachate was measured. If the Cr ion concentration was low and no color interference occurred, the Cr was shielded with NaAsO ₂ and titrated with the ammonium ferrous sulfate method. If the Cr ion concentration is high, the concentrations of V ₂ O ₅ and Cr are continuously measured by a continuous measurement of vanadium chromium.

Second, the experimental results and discussion

(1) Exploratory experiment

The high-chromium vanadium slag was firstly ground and then subjected to exploratory experiments. The vanadium-containing chromium mud was leached with H ₂ SO ₄ and NaOH respectively. The liquid-solid ratio was 2:1, the leaching time was 60 min, and the leaching temperature was 95 °C. The results are shown in Table 2. It can be seen from Table 2 that H ₂ SO ₄ can effectively dissolve vanadium in the chromium mud, but the amount of acid is large, and the eluted Cr ₃ ⁺ needs further treatment, which is extremely inconvenient. During the experiment, it was also found that a large amount of gelled matter was present in the acid immersion liquid, which made the leachate have poor filtration performance. In the alkali leaching experiment, a certain amount of NaOH can make the V ₂ O ₅ leaching rate reach 68.50%, and the selectivity is strong, and Cr ₃ ^{+ is} not dissolved. This result is different from that reported in the literature.

Exploratory experiments have shown that due to the disadvantages of high acid consumption and poor filtration performance of the leachate in the acid leaching process, it is not appropriate to use the acid leaching process to leaching V ₂ O ₅ from the chromium mud. The alkali leaching process is highly selective and the V ₂ O ₅ leaching rate is high. Therefore, for the chrome mud, it is preferable to extract V ₂ O ₅ by the selective alkali leaching process.

Table 2 Exploratory leaching results of chrome mud

(2) Single factor experiment of NaOH leaching

1. Effect of NaOH dosage on V ₂ O ₅ leaching effect The effect of NaOH dosage on V ₂ O ₅ leaching effect is shown in Fig. 1. When leaching, the liquid-solid ratio is 2:1. The leaching time was 60 min and the leaching temperature was 95 °C.

Figure 1 Effect of NaOH dosage on V ₂ O ₅ leaching rate

It can be seen from Fig. 1 that as the amount of NaOH increases, the V ₂ O ₅ leaching rate also increases. However, when the amount of NaOH reaches 30% and continues to increase to 50%, the V ₂ O ₅ leaching rate only increases from 68.50% to 72.30%, and the increase is not obvious, indicating that the V ₂ O ₅ leaching rate when the NaOH dosage reaches 30%. Has already tended to the limit.

2. Effect of leaching time on V ₂ O ₅ leaching effect The effect of leaching time on V ₂ O ₅ leaching effect is shown in Fig. 2. When leaching, the amount of NaOH is 30%. The liquid-solid ratio was 2:1 and the leaching temperature was 95 °C.

Figure 2 Effect of leaching time on V205 leaching rate

It can be seen from Fig. 2 that in the initial stage of leaching, the leaching rate of V ₂ O ₅ is more affected by the leaching time. Between 20 and 60 minutes, the leaching rate of V ₂ O ₅ increases rapidly, from 37.90% to 68.50%, 60min. After that, the effect of the leaching time is significantly reduced, and the V ₂ O ₅ leaching rate hardly increases.

3. Effect of leaching temperature on V ₂ O ₅ leaching effect The effect of leaching temperature on V ₂ O ₅ leaching effect is shown in Fig. 3. When leaching, the amount of NaOH is 30%. Liquid to solid ratio 2:1. The leaching time is 60 min.

Figure 3 Effect of leaching temperature on V ₂ O ₅ leaching rate

As can be seen from Fig. 3, the leaching temperature has a large influence on the leaching rate of V ₂ O ₅ . At a temperature of 40 ° C, the V ₂ O ₅ leaching rate is very low, only 36.70%, and when the temperature is raised to 95 ° C, the V ₂ O ₅ leaching rate is significantly improved, which is 68.50%.

4. Effect of liquid-solid ratio on V ₂ O ₅ leaching effect The effect of liquid-solid ratio on V2O5 leaching effect is shown in Fig. 4. When leaching, the amount of NaOH was 30%, the leaching temperature was 95 ° C, and the leaching time was 60 min.

It can be seen from Fig. 4 that the V ₂ O ₅ leaching rate is not greatly affected when the liquid-solid ratio is less than 5:1, but as the liquid-solid ratio continues to increase, the V ₂ O ₅ leaching rate tends to decrease. This is because, when the liquid-solid is relatively low, although the viscosity of the slurry is high, which is not conducive to the leaching reaction, the NaOH concentration is relatively high, and the effects of OH ^- and v (IV) or v (V) are significantly stronger than the viscosity, therefore, The V ₂ O ₅ leaching rate is also relatively high. When the liquid-solid ratio is increased, the effect of OH ^- and V (IV) or V (V) is weakened, which is not conducive to the leaching of V ₂ O ₅ .

Figure 4 Effect of liquid-solid ratio on leaching rate of V ₂ O ₅

(III) Oxidation alkali leaching experiment

In order to further improve the leaching rate of V ₂ O ₅ , the effect of the alkali leaching process on the leaching of V ₂ O _{5 in the} chrome mud was studied. In the experiment, V(IV) was oxidized to V(V) by two different oxidation methods, namely direct alkali leaching oxidation and oxidation under weakly acidic conditions, the former using H ₂ O ₂ as the oxidant and the latter using KC1O ₃ .

1. Effect of H ₂ O ₂ dosage on V ₂ O ₅ and Cr leaching rate The effect of H ₂ O ₂ dosage on V ₂ O ₅ and Cr leaching rate is shown in Fig. 5. The leaching conditions were: 30% NaOH, initial liquid to solid ratio of 2:1, leaching temperature of 95 ° C, and leaching time of 60 min. It can be seen from Fig. 5 that during the alkaline leaching oxidation process, the Cr leaching rate increases due to the increase of the amount of H ₂ O ₂ , and the leaching rate of V ₂ O ₅ shows a different law: when the amount of H ₂ O ₂ is low, The V ₂ O ₅ leaching rate decreases until it reaches a certain level. This may be due to the presence of a large amount of Cr(OH) ₃ in the leaching system, so that H ₂ O ₂ preferentially oxidizes Cr(III) and consumes a certain amount of NaOH during the oxidation process, thus lowering the V ₂ O ₅ leaching rate. As the amount of H ₂ O ₂ increases, Cr(III) and v(IV) undergo competitive oxidation, so the V ₂ O ₅ leaching rate begins to increase.

Fig. 5 Effect of the amount of H ₂ O ₂ on the leaching rate of V ₂ O ₅ and Cr

2. The effect of KC1O ₃ dosage on V ₂ O ₅ leaching rate is 10% H ₂ SO ₄ in liquid-solid ratio to create acidic conditions. Potassium chlorate is added for oxidation. The temperature is 95 ° C, the acid oxidation time is 60 min. After oxidation is completed, NaOH leaching is performed. . The amount of NaOH is 30%, the leaching temperature is 95 ° C, the liquid-solid ratio is 2:1, and the leaching time is 60 min. The effect of the amount of KC1O ₃ on the leaching rate of V ₂ O ₅ is shown in Fig. 6. Since Cr (III) has strong stability under acidic conditions, Cr is not detected in the alkali immersion liquid, and therefore, Cr is not measured.

Fig. 6 Effect of KClO ₃ dosage on leaching rate of V ₂ O ₅ and Cr

It can be seen from Fig. 6 that the alkali leaching rate of the high chromium vanadium slag after oxidation under acidic conditions is remarkably improved. When the amount of KClO ₃ is 1%, the leaching rate of V ₂ O ₅ is 71.4%, and when the amount of KClO ₃ is 2%, the leaching rate of V ₂ O ₅ is 79.3%, and when the amount of KClO ₃ continues to increase, V ₂ O ₅ The increase in leaching rate is not obvious.

Third, the conclusion

(1) For the vanadium-containing chrome mud studied in this paper, acid leaching is not suitable due to the high acid consumption and poor filterability of the leaching solution.

(2) The alkali leaching process can better leaching V ₂ O ₅ in the chromium mud. The suitable process conditions are: 30% NaOH, 2:1 liquid-solid ratio, 95 ° C leaching temperature, and 60 min leaching time. At this time, the V ₂ O ₅ leaching rate reached 19.50%.

(3) Compared with the direct leaching process of alkali leaching and the weak acid oxidation-alkali leaching process, it is found that the direct oxidation of alkali leaching has the disadvantage of poor selectivity and the leaching of Cr in the leaching process. A large amount of H ₂ O _{2 is} required to improve V ₂ O. ₅ leaching rate. In the chrome mud oxidized under acidic conditions, the leaching rate of V ₂ O ₅ is greatly improved when alkali leaching, and can reach 79.30.

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